Iran's president is blaming the United States and its Gulf Arab allies for the brazen attack on a military parade in southwestern Iran that killed at least 25 people and wounded nearly 70.
"All of those small mercenary countries that we see in this region are backed by America," Iranian President Iranian President Hassan Rouhani said Sunday without identifying any countries. "It is Americans who instigate them and provide them with necessary means to commit these crimes."
Rouhani, speaking before leaving Tehran to attend the U.N. General Assembly, said, "America is acting like a bully towards the rest of the world." The Iranian leader said his country's response to the attack is "forthcoming within the framework of law and our national interests." He said the U.S. would regret its "aggressiveness."
The U.S. ambassador to the U.N. Nikki Haley condemned the the deadly attack but said the country's rulers need to look at their own base for the reason behind the unrest.
"He [Rouhani] has oppressed his people for a long time and he needs to look at his own base to figure out where that's coming from," she told CNN on Sunday. "I think the Iranian people have had enough and that's where all of this is coming from. He can blame us all he wants. The thing he's got to do is look at the mirror."
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U.S. State Department spokeswoman Heather Nauert said, "We stand with the Iranian people against the scourge of radical Islamic terrorism and express our sympathy to them at this terrible time."
Officials said two gunmen died and two other suspects were arrested after the Saturday attack.
Both Islamic State and a group calling itself the "Arab Struggle Movement for the Liberation of Ahvaz" claimed responsibility for the shooting in Ahvaz in Khuzestan province.
State television said the assailants targeted a stand where Iranian officials had gathered to watch the annual parade commemorating the launch of the Islamic Republic's 1980 - 1988 war against Iraq. Similar parades were held across the country.
Most of the dead were said to be members of Iran's elite Revolutionary Guard. Some reports said one of the dead was a journalist.
Reuters, citing Iranian state media, says Iran's government summoned the envoys of the Netherlands, Denmark, and Great Britain Saturday, accusing them of harboring Iranian opposition groups in their country
Iran's Supreme Leader Ayatollah Ali Khamenei said the attack was linked to the United States' "allies in the region," and he ordered security forces to bring those responsible to justice.
"This crime is a continuation of the plots of the regional states that are puppets of the United States, and their goal is to create insecurity in our dear country," Khamenei said in a statement published on his website. While he did not specify exactly who the states are, U.S. allies in the region include Iran's main nemesis, Israel, and Arab Gulf states, particularly Saudi Arabia.
Foreign Minister Mohammed Javad Zarif blamed the attack on "regional terror sponsors" and "their U.S. masters."
Zarif said Iran would retaliate "swiftly and decisively" to the attack.
Khuzestan borders Iraq and has a large ethnic Arab community, many of them Sunni, in mainly Shi'ite Iran.